I used to give Momo bully sticks to chew on while I groomed him.
Otherwise, he'll attack the brush & whatever grooming tool I was using. He still does it now, but he'll tolerate it as long as I don't pull on a tangle, so I just cut it off.
It's best to shave the under belly, arm pits, inner thighs, those are high rubbing areas which tends to tangle. They're sensitive areas also, so it's best to cut off the tangles w/a blunt nosed scissor instead of working it out. It's imperative that grooming time should not = ouch time when they're young pups. You want them to associate grooming time as special bonding time w/mommy or daddy. No scolding, only praises when she's good. If she acts up, give her a break.
You can give her a bath & use a lot of conditioner. Massage the conditioner into the mats, really work it in & let the conditioner sit for 5-10 mins. You can wrap her in a towel while waiting so she doesn't get cold. Rinse well.
Dry her completely w/a human dryer or pet dryer. Once the hair is 80% dry, you can brush the tangles out. It's harder to brush wet hair & it breaks easily. If it's a stubborn tangle close to the skin, you can snip once or twice w/blunt nosed scissors (some people prefer thinning shears), loosen it & brush it out. A conditioning/ detangling spray directly sprayed on the mat also helps loosen it.
Line brushing works great. If you're not familiar w/it, that's when you pull up a section of hair & brush downwards in layers, working your way up. Brushing this way ensures that all the hairs are smoothed out. The brush will also go through the hair easier, little at a time & it doesn't pull on their sensitive skin. This works especially great on the legs, where they tend to tangle & most people don't really pay attention to that area.
Hope that helps!