Sorry to hear you are both going through this, OP. Or all of you, if there's more than the two of you in the family.
In our case it wasn't a case of relenting. As others have said, it's not a miracle cure. It was a serious decision taken after a long period of discussion with the CAHMS team, based on a risk assessment weighing the risk of side effects against the risk of further suicide attempts, and part of an extensive therapy programme. Which is actually exactly what you seem to be describing too, OP. You are not talking about giving in and buying sweeties for a tantrumming toddler, you have explored all avenues and nothing seems to be working so far.
In dd's case she had already been doing the therapy for quite some time and it was absolutely clear she was incapable of engaging but the doctors were holding out for her 15th birthday with the antidepressants.
Things didn't magically clear up after starting the medication, and she's had a couple of false starts where she's either had to change medication or had bad side effects with a new one. She made one suicide attempt after (but probably not caused by) going on meds. She has had more panic attacks than she can remember, some of them in awkward places (the tube at midnight, coming back from a party).
BUT- and this is a big but- with the help of meds she was able to engage in the programme and work on a supported part-time return to school. She got enough GCSEs to get into college. She did well there.
In dd's case (23 now) she will probably never be off the meds as her MH issues are linked with a chronic physical disorder as well. But she is coping. She held down a job for 2 years after college, she is now studying the thing she has dreamt of all her life, she is hoping to forge a career in a very competitive industry. She knows she has to work with her MH issues as well as with her physical disability and has developed a whole skills set for doing that. It's good enough.