Did she taper off the Paxil, or just switch abruptly? If the latter, it's most likely withdrawal from Paxil, which is known to have strong withdrawal effects. Taking another med even in the same class won't necessarily, or even usually, do anything about withdrawal from a prior med. It's also very difficult to tell which effect is withdrawal and which is a side effect of a new med if you just switch from one to another without tapering off the first med before trying the second.
She needs to give the medication more time, but I would also discuss this with her doctor. Normally it takes up to 6 weeks to get the full benefit of a new medication.