What would be your best advise for a RN who has been out of an acute care setting for over 20 yrs doing Home Health considering try to get a job in a LTAC or Rehab center.

With that much experience in HH you would def have enough knowledge to look at a manager position with a HH co or even a DME co. Or have u considered being a case manager?

As a new nurse, is it okay to go from specialty to specialty (new job to new job) within the first year, for the sake of knowing what your niche is? Im currently in rehab nursing but I dont feel like this job isnt giving me the experience I need.

Don't! Stay where you are and enjoy your life. Non-medical staff now runs medical staff. The emphasis is on profit not bedside care. Short-staffing is commonplace according to budgetary concern. Administrators get big bonuses when they stay under budget.
In experience in acute care setting combined with inadequate orientation training allotted you are risking everything you worked for.

I would vet the LTC organization and survey history. Look for 12 hours 3 x per week; the staffing matrix sees if they're using many agencies that will impact your work. LTC uses PCC, which is a computer program and pretty easy to use. Notably,
the pay demand for years of experience request sign-on bonuses. What do they do for the staff to keep the morale up and engaged?
Let me know how you make out. The LTAC is stressful, understaffed, lack staff education and training, and will be on your feet all day. The patient load is very complex, typically post ICU, and unstable in general, and many wounds drip, etc.; start in a subacute where you can home your skills, and even where they have LTC and subacute is excellent well. Never allow any organization to dismiss your twenty years as an RN.
Vincent

If that is what you want go for it, remember that you have to be on your feet a lot more and have to complete your duties in a timely manner. Time management is key to success