My 4yo will be getting yet more Lego, small Sylvanians and Playmobil sets to complement what she (and her older sister) already have, beginner stilts (she has the cups with ropes already and is ready for a bigger challenge), a LOL pet, another polly pocket, and some books.
The marble run suggested up thread is a good choice as are the easier board games like Hungry Hippos, Fishing/hook a fish game, Buckaroo, Pop up Pirate, Guess Who, and Kerplunk (we have all of these already). We also taught both her and 6yo DD1 how to play Uno this summer which they are both now obsessed with, and I know they would enjoy the Dobble we have in the cupboard too if they ever allow another card game get a look in!
She also likes My Little Pony, dress up, and Shopkins (these are extortionate new and crap IMO, but you can buy a job lot second hand very cheaply)
If your DD likes the Peppa figurines & playsets, it might be worth trying Sylvanian Families: very cute with smaller and more detailed accessories than you get with Peppa. You can often get cheap discounted sets in TKMaxx, or FB Marketplace if you are happy with second hand. They are really well made (DCs have my childhood Sylvanians as well as their own as mine have lasted) and would offer a good longevity of interest.