Does she have a prepaid or postpaid account?
If she has a postpaid account:
Roaming should be active by default if she has a postpaid plan above 599.
If she has a prepaid account or has a postpaid plan 599 and below, they can activate it through My Account. They can also Tweet @talk2globe to facilitate their request. In addition, they can call +6327301212 (Toll Free for Postpaid. Charges may apply for Prepaid) using their Globe Mobile Phone. Note: For prepaid account, there should be at least PHP 100.00 in their account in order to activate Roaming.
If you ask me personally, I'd activate roaming via Twitter or My Account instead just to be on the safe side.
I hope this helps!
if you are here in the Philippines, you may call 211 to request for activation of Roaming service of your mom.