M.W.
I would stop using it when she either outgrows the weight limits (don't want it breaking on her!) OR when she is able to get herself out of it (don't want her falling out).
Other than that, I wouldn't worry about getting rid of it if she enjoys it. Unless it's just a pain in the (you know what) to keep it out, or it takes up a beastly amount of space.
If you are just using it as a safe place to keep her while you are trying to get other stuff done... maybe you could switch it out for an exersaucer or jumper play-thing.... or one of those baby 'corrals'. I bet you could sell it on craigslist, and find a new toy fairly cheap. :)