I don't think I'd use the slicker brush on her unless her coat is longer and free of mats. They can actually be painful for some dogs, so you might consider getting her a brush similar to this:
Amazon
That's what I use for Billi and brushing her got a lot easier, she tolerated it better. We also use the Viva La Dog Spa products and they're great!! Make sure the mats are really saturated before combing and just go slow with it. She's probably uncomfortable so I'm sure she's getting impatient about it. If any are too bad, you might just snip a piece of the mat to comb the rest of it out. You can also just saturate the mat with conditioner and do it that way before her bath.
Mats are the worst, but you'll get 'em! Good luck with it!!