My dog is constantly licking her tush?

Sounds like anal glands. It is possible to manually express them, externally, by pushing either side of the anus. Stand clear as if she is clogged, it may well squirt out.

These glands are scent glands and provided her stool output is normal, should express a little of the fluid in them with every passing of a stool. When there is a period of abnormality they can become clogged and infected and if left, can even rupture. The dog wil be uncomfortable, and you will smell a fishy aroma back there too. The vet should manually drain the glands and see what comes out. If there is infection he'll do a 'flush and pack' (with antibiotics) to clear it up. You might need to adjust her diet to produce a more normal stool or as these glands will always refill - they should never be empty, the same thing may happen again.

Most dogs go through their entire life without these needing to be touched. There is no need for them to be regularly drained.

Please don't use any home-treatment and no collar..... I can't imagine having an itch I can't scratch!!

If she's licking down there you need to put on a lamp shade satellite dish buster collar immediately so she cant. Temporarily you can use preparation H or something similar for humans in a small amount mixed with polysporin (only if she's wearing the collar) which will provide relief but she probably needs anti biotic's and/or an anti fungal topical cream prescribed by a vet. If you wont do human ointments than you can put the buster collar on but she might just going to drag her but on the floor if its irritated.

My dog licks his bits too. Shes probably cleaning herself, it seems normal. But as a worried owner you should check her out just incase. Better safe then sorry! Hope all goes well :)