Be Brave
Go to the park mid day mid week when it is quiet and make Holly sit and wait, then unclip the lead and say STAY.
She MIGHT, with luck, be so surprised by the change of routine but firmness in your voice (no trepidation or wondering if this will work) and then say Go PLAY and wave her off.
She will bound away but have a really tasty treat in your bag or a squeaky toy and then call her back in a high pitched, squeaky, really excited voice, squeak the toy like mad and flap your arms welcomingly as she runs back, big cuddles and the treat when she comes. Don't worry what you look like. You have joined the mad gang of dog owners who are trying to train their pups.
Mum is now lovely to come back to. Practice this for ages and she will love it (at 4 months), by 8 months she will be a teenager and not come near at all
Another brilliant idea we were told by Jack's trainer was to go to a quiet wood with bushes. Let her off the lead and when she's not looking, hide and call her. This is the only time you frighten your puppy. She will panic and try to find you. You then reward her with lots of loving and treat when she does. Practice this a lot, including playing Hide and Seek behind trees and make it a game. She will always think you are so stupid and get yourself lost so easily she had better keep an eye on you at all times
This has worked for Jack, who is now 18 months, and he will always come back to us (eventually) reinforced with whistle training as soon as you can. I still play Hide and Seek with him, much to other walkers' amusement, but what the heck..
Now Becky is a different kettle of fish and has no flipping recall because we rehomed her at 10 months and all she seems to have learnt is that if she came then she would get locked up or beaten we think. She keeps right out of arm's reach at all times.

Flipping exasperating collar dodger
We were taught that you have a window of opportunity up to 12/16/20 weeks when a puppy's brain is a sponge soaking up instruction and information that will last him/her for life. Essential to get cracking on off lead training now and be brave. Just be careful you check out for hazards before you start training - no roads, animals, cliffs, water etc.
Good luck and have fun - your doodle will
