I like just using a good human hair shampoo+conditioner (when it's warm enough to bathe). I leave the conditioner in for 10-15 minutes (until the hair has really soaked up most of the conditioner) then I rinse it out. The hair is usually silky soft after that and generally stays that way for a few weeks, months if you bag it.
Showsheen is also great for short term use, it might be good to try while it's still cold out.
I'm not a huge fan of it over the long term because the silicone in it (the stuff that "coats" the hair) makes it difficult for other products to penetrate the hair shaft after Showsheen has been used. Basically, over the long term, the hair ends up getting super dried out because nothing good can get in there. :(
I also really like Cowboy Magic detangler. It's a little greasy for manes that aren't crazy thick (it might be great for your girl's mane though!) but it's fantastic for tails. I've also seem WD-40 work well and make manes/tails softer but it does stink.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.