I think a nosegay would be very appropriate- small enough to fit in a tall glass so no one has to hunt up a a vase.
I would hate getting a picture frame. Flowers are fine. They last a while they are pretty, but you don’t feel obliged to use them to prove you are grateful.
I have a friend who has brought me the same tea towel twice - for the same favor - she comes to me on the train I drive the rest of the way to the high school reunion. Anyway, I’m happy to get the tea towel and this year also pot holders crocheted by her Mom, but the best thank you from her was actually what she sent me afterwards which was a paperback fantasy novel that we’d talked about on the drive. Which is just to say, sometimes the best gift is the really, really personal one.
If I were your former boss, I would love getting the flowers. No one ever gets me flowers, not even DH. But, if I was having a bad allergy day (the air quality was bad or something), then I would probably toss them sooner than needed because I would be sneezing. I would still love the thought that someone brought me flowers.
Instead of cut flowers, I bring a small potted plant. Orchids, succulents, seasonal… depends on the situation and availability. No need for the host to search for a vase. I do think that would be appropriate in this situation since you’re going on a tour of the town, which is very generous of your former boss to offer to guide/accompany you on.
If the relationship was purely professional, why the meet up in the first place? What has her DHs job (or what they earn or how fancy the condo is) got to do with it? Is this a networking thing? It sounds uncomfy.
What is wrong with meeting with a former boss? We had a lovely dinner with Mr.'s ex-CEO and his wife - we were visiting their new town and dropped them a line. They were super excited to show us their new house and the area. We knew they were into good red wine, so we brought a couple of local bottles that made the top 100 wines of the year list. It was not weird or uncomfortable at all.
I suspect your DH wasn't hand wringing about the meet up protocol.
OP may be hand wringing because she feels she is “socially awkward,” not because it is strange or wrong to meet former boss socially.
I have quite a few former managers I would get together regularly, and there are some I wouldn’t even want to say hello if I saw them on the street. I have a feeling OP and her former boss got along pretty well before she moved away.
Lol, there are some bosses I don’t even care enough about to hear how they’re doing. But it’s not uncommon today to have some pleasant relationship, whether it’s same gender or opposite. It’s very individual and nice to think we’re comfortable enough to make the contact, in another location. No need for it to be “networking” or odd.
We should give each other credit for being grown ups in this era.
It’s a nice contact and some are better at it than others. Flowers (or a small plant) are pretty, simple, and just a nice thought. If you’re worried about a vase, get something that comes in one. There are all sorts of small hostess gift sorts that do.
Let’s just not change this simple set-up to a big problem in our minds.
About lunch. If she suggests some place casual and inexpensive, you can offer to pay. See what happens. To my thinking, after all, she’s taken time to tour you. Or she may say, but you’re the guest in my area. Good manners, on her part, shouldn’t be the uber expensive restaurant.
You always have the polite opportunity to say, let’s just have coffee (or something light,) because you have dinner plans. That’s ok, among two reasonable ladies.
Have a great time.
I second the idea of giving flowers in a small vase or wood box or such.
I love flowers in my home but do not like getting them when not expected
and dealing with vases and such.
Thank you, everyone. We’ve already met and unfortunately I didn’t have a lot of choice because all the flower shops were closed on Sunday, so I just got tulips at Whole Foods. And it was raining so walking tour didn’t happen, they reserved a restaurant and took us out for lunch. I might have been somewhat misleading when I said we had a strictly work-related relationship because we’ve been friends on Facebook for a while and exchanged comments and such. We’ve known each other for a long time and she was always quite informal and loved to talk about her family. I didn’t have any actual networking in mind but did get a lot of information related to the city and local colleges. It was lovely and we had a great time (except probably DS who was somewhat intimidated 
)
Tulips from Whole Foods sounds like a nice gesture - I’d be full of smiles to receive them! Who doesn’t love tulips!
Hope it all felt pretty natural and not awkward!
my very favorite flower!!
Awesome! Anyone can bring me tulips any time of the day. I’ll pour you a glass of nice wine. Thanks for the update, and it sounds you had fun!
Glad you had a nice time! I’m sure the tulips were perfect.