Being assigned another autistic persons caretaker

I really enjoy theatre, and I'm often involved in local community theatre projects. However I have a frequent problem that occurs in learning and am-dram settings where I almost always end up assigned to take care of someone who has more obvious autism than I do. I was diagnosed when I was 13 and am now in my late twenties, and I've spent a significant amount of time learning how I can best accommodate myself. 

I've experienced before people pretending I don't exist so they don't have to deal with me, and I don't like to make other people feel that way, so when I see someone in a theatre space struggling to pick things up like their blocking/character intentions/dance sequences, then I help them out. Multiple times this has meant this person starts to cling to me to learn all their work for them and break it down, they need me to reassure them and encourage them constantly and honestly it's exhausting. It also often makes it harder for me to socialise with the wider group as they don't want to engage with these people, who frequently drop large amounts of personal and upsetting information on you without prompting and they don't show much interest in other people. 

Today at a rehearsal I was trying to learn some new dance routines, and it was clear I'd been paired with a much older woman who is very open about her autism to help her pick things up. I was struggling to learn the dance myself and at the same time I'm breaking it down in various ways to try and help her to understand, even drawing out the whole routine for her, all the while she's telling me deeply personal information about herself. I felt really uncomfortable but she's said so many times that if it wasn't for my help, she'd be too discouraged to continue and quit. I'm too overwhelmed by my own life to spend my spare time taking care of another autistic adult, and I really don't feel like it should be my job, but I don't know how to tell her or the directors this without making her feel like there isn't a place for her in theatre which I want to be a more accommodating place. 

Does anyone have any advice for setting boundaries with other autistic people? I don't feel like it's fair that I have to ignore my own needs to make others feel accommodated in these settings.