Hope she recovers. If it should turn out she takes a turn for the worse, if she's very close to birthing you may be able to save the fry, even if it means using gently squeezing her to expel them from her body, or even sterile sharp scissors to cut them out, being very careful of course not to damage the fry, as they are packed in there tighter than sardines in a can.
I'd suggest those only a last resort if Mom does not do well.
I'd suggest it might help to have some Indian Almond leaf in her tank, it has natural antibiotic properties than may be helpful but a very severe fin rot often will require antibiotics to cure it. Don't waste money on OTC stuff that has tea tree oil, it won't help with advanced fin rot, though it can help prevent it in a clean tank.
Keeping water conditions as pristine as possible help also, so those changes are good. Fin rot is often due in part to some problem with water conditions. Have you tested the water recently and if so, what were the results ?
Best of luck, hope you get healthy fry at the least.