Little dogs

[tilly]

Hiya
My dog has recently been displaying aggression/dominance at small dogs. This started because she was socializing with a dog that frequently attacked small dogs.
My dog now sometimes (only sometimes) will try and pin down small dogs. There are certain types of dogs she will do it too:

• Norfolk/border terriers (this is because an incident happened with the dog she was socializing with and 2 terriers)
• Jack Russells (only some - there are a few she is fine with)

I have noticed that she does it to slow/timid/elderly small dogs that are walking slowly. I was thinking this might be because she has a high prey drive? However she is normally fine when small dogs are running around?! It's as if she can't deal with the slow/weak energy? I know dogs don't like weak energy and will try to get rid of it - but how can I get her accustomed to it?
Please note - she has many small dog 'friends'.
Any tips or advice to deal with this?

Thanks