Hen cant walk and when does wobbles with butt in the air.

[Wyorp Rock]

I have rooster booster on the way, should be here tomorrow.

I'd go to Walmart, CVS, etc. and pick up a bottle of B-Complex and Vitamin E as suggested.
While Rooster Booster is fine to give, check your label, it will be lacking in the therapeutic amounts of E and B's that were suggested. The RB Vit/Electrolytes analysis per OUNCE of product, it's misleading and even if you gave that huge Ounce amount, you'd only get to 160UI Vitamin E.
Same with RB Poultry Cell - analysis is per OUNCE and then that will only give you 50IU Vitamin E.

If your hen is not able to walk, I'd start her on B-Complex which should have all 8 B Vitamins, give her 1/4 tablet daily along with 400IU Vitamin E. Give her a treat of egg to help with the uptake of E and give a little protein boost.

Yes, it could be Marek's disease or a 100's of other things. Marek's affects young birds for the most part. Symptoms of Marek's usually is seen from 12-40weeks of age, but that's an average. Possible the Pullets brought something in with them or you already had Marek's in your flock and stress brought of adding new birds caused some shedding or or ... again - there's a lot of factors.
Depending on how "hot" the strain is, it can wipe out a lot of birds. If the strain is relatively mild, then likely just weaker birds will become symptomatic and/or die.

If it is Marek's why are the rest of my bird not affected? It's only been my younger ones (less than a year) after I bought the 14 pullets in March of last year. I'm not saying it isn't I just thought it was really contagious.

Read your labels!

Rooster Booster POULTRY CELL