Generally colleges want recommendations from two teachers in core subjects: one STEM, one humanities (this may vary a bit between colleges, but is often the best strategy, especially with competitive schools). Some colleges allow an optional third LOC - that one could be from the theater teacher, but it would be optional.
This worries me a bit. You certainly want to avoid leaving the impression that she is not the “ideal student” she used to be leaving open the possibility that she has not overcome/mitigated her mental health struggles. You need to reassure colleges that she will be successful at the college and not leave open the possibility that she is no longer as capable of doing that. For this reason, I would think it all the more important to get an LOC from a RECENT teacher who can speak to her ability to succeed NOW and not three years ago.