Yeah - sounds just like both of my girls (now 4.5 and 2.5). For a while I did bring in lots of new stuff - from consignment and garage sales. (allowed me to rationalize "well at least it dosn't cost a lot".) But, i wasn't happy with the interaction it set up - always needing new stuff to keep us interested.
We finally hit upon several things, although they might have both just grown out of it, because things got better from both of them as pretend play developed.
1) let them get into your stuff. Seriously - trotting around the house in one of my pairs of shoes (flats) was good for at least 1/2 hour. Add in a scarf, or a pair of gloves that instantly became puppets, and I might actually get dinner on the table. Other stuff too. My pots and pans and my spoon were way more exciting than the kitchen set that they had.
2) consider messy play - paints at an easel were good for a big while - esp. if you are not picky about making BIG plops of color on the paper. I found a wet birds eye diaper was indespensible at times like these. It sucked the mess right up! Play dough - homemade is messier than Dream dough brand, which stays together better than the other brands, IMHO. Waldorf-style beeswax is the least messy, but neither of my girls could do much with it at that age.
3) consider even messier play - if you are willing, a large tupperware storage box with a few inches of sand in the bottom is GREAT - even just for the novalty in the winter. this entails vaccuming, though, so YMMV. Some people do this sort of thing in the bathtub - you still have to vaccume, but the mess doesn't get tracked all around the house if you get pulled away before it is all clean.
4) combine more than one toy - are there two puzzles that are mastered and forgotten? combine the pieces for a new challange
5) homemade stuff - for some reason, little cheesy paper puppets that I made one rainy day are the ones that keep getting pulled out. I taped together a few small boxes to make a dollhouse once - that one still gets used, the nice wooden one has become the storage place for all the dolls and animals. Ah, the money I could have saved. . .
6)best of all - forget the toys and let her help you! sorting socks was a favorite activity at this age. A baby washcloth wet with just water sent each of my girls of on a mission to "wash the floor" don't even get me started on the short broom.
also - I've found that by afternoon, nothing looks exciting anymore, so that is where we put our bathtime. after that, they seem to recharge and think of what might be in store for later. . .
You can get creative in the tub too. A fav around here is ice cubes. Either plain or colored with a little food coloring.
If I think of any more, I'll share.