How about calling or emailing her and telling her exactly what you reservations are? Be straight with her. You aren't sure you can trust her considering how things ended so abruptly last time.

I, personally, would have no qualms about going back to my old therapists, BUT, they were entirely consistent. We ended on mutual and positive terms. They were all quite helpful in their own ways. So I don't have that bad ending issue you speak of.

If, after discussing that with her, you feel reassured about it, then perhaps a session or two (maybe alternate between the two therapists for a few weeks?) and get an idea if you feel like you could/should go back. Sometimes we think it's a good idea, but when we go back it doesn't feel right -- it feels stuck in the past. On the other hand, if it feels like you can continue good work with the old therapist, then it is up to you to decide. You'll have options.

As for as your current therapist goes, it isn't your job to worry about her. She'll be fine either way. I doubt you would be treating her "shabbily." You would just explain your decision and go with your best instinct.