A kitten won't be able to jump that high, but kittens are the best climbers in the world. If you don't want her to climb up via the mattress, sheets and blankets, put a small cat tree or carpeted climber next to the bed. She might decide to use that, or she might prefer the mattress/sheet/blanket route. She'll make her way up, no doubt about that.
(I saw a 5 week old kitten climb over a 3 foot tall mesh child gate once. When there is a will, they find a way)
She may not be able to really jump right up, but she will try and at least scramble up. I would not build her anything to come up on the bed. Give her a month or 2 - she'll come up when she wants to.
Course I told my little 4 month old rex kitten she was too little to go from the table to top of curio cabinet like the adult rexes do. Next thing you know she is up there and can't get down herself. So I got her down and watched - that little rascal made a flying leap on the GLASS front and somehow scrambled up the rest of the way. I thought it was impossible for cat paw pads to stick to glass for climbing!
cats are so fast sometimes thay can scale hard things with their claws. My cat jumped from the stairs onto the back of our big screen sony( I think it's 45 inch)projection tv and instead of falling down he was able to come over the top. It was a big thud and then that scratchy scramble noise you hear while you hold your breath lol
Aya-chan is about 10 weeks old and while she can't leap that high she can certainly climb. Those things we refer to as 'claws' make pretty good climbing aparatus and she scales my laundry hamper and 6 foot bookshleves just fine. Don't know how to get down though.
My kittens are 4.5 months old now and have no trouble at all jumping up on the bed. I didn't really keep track, but I'm pretty sure they were getting themselves up there by the time they were two months old, maybe younger.
Shareena, my smallest cat, made the jump to the kitchen counter when she was 3 months old, right after I told her it was too high for baby kitties.