Etiënne Nothing will change about her account. The pack only makes it so that she doesn't have to pay fees for her plan (Easy Bank or Easy Money) anymore. Otherwise, the pack doesn't connect your accounts in any way.
She will still have to pay incidental fees by herself (for example for withdrawing money at an ATM more times per month than is included in her plan) and if she's using Easy Green, she still has to pay the difference between Easy Money and Easy Green plan by herself.
She can also decide to leave the pack and pay for her plan by herself at any time in the future. It's very similar to subscription plans like the Spotify Family pack etc. -- the individual members still have their own account, their own listening history etc. they just don't have to pay for the Premium subscription by themselves and with the bunq Pack the same is true: the members have their own accounts that they can do what they want with and nothing gets disclosed about their payment behavior etc. to the owner of the Pack, only their plan fees are covered by it. That's also the reason why so many people share their bunq Pack with strangers here: https://together.bunq.com/d/26999/1563 It's an easy way to safe some money.
I hope this answers your questions, if not feel free to ask again. Also check out the information pages from bunq: https://together.bunq.com/d/313