Peace be upon you and God's mercy and blessings.
Ayatollah Khamenei (may God protect him):
If a fasting person intentionally submerges their entire head in water, it is strongly recommended that their fast is invalidated, and they must make up that day's fast.
Therefore, your daughter has two options:
First: To exercise caution and avoid submerging her head during the day in Ramadan.
Second: To follow the ruling of someone who states that it does not invalidate the fast, like Sayyid Sistani, while considering the most knowledgeable in this matter as a precaution.
Ayatollah Sistani (may God protect him):
There is no objection to swimming, even if it requires submerging the head, as per His Eminence (may his shadow endure), submerging is not one of the invalidators of fasting, although it is highly discouraged.
May you be successful in all good.