HoT account swap?
It is against the ToS to transfer ownership of an account, meaning that your mother cannot just give you her account. It’s also not possible to transfer an account key from one account to another, so no you won’t be able to shift her HoT over to your account.
If your mother doesn’t want her account and it was purchased recently she may be able to get a refund on the purchase and if she’s kind then use that refunded money to purchase HoT for you?
If HoT was purchased within the last 30 days and directly from ArenaNet (buy.guildwars2.com), then the account holder can request a refund to revert the account. You can then buy HoT, on sale.
Yup. Best thing to do is have your mother request a refund so you can use the cash to buy a brand new Heart of Thorns key for yourself without wasting anymore money.