Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear sister, thank you for your question and your care about your daughter.
Regarding your query, piercing ears for women is permissible as there is no evidence in the Shari`ah to prohibit it.
Responding to your question, Sheikh Kifah Mustapha, the Imam and Associate Director at the Mosque Foundation, one of the largest Islamic Centers in Chicago, states:
The general rule in Islam is that: all matters are permissible unless there is an authentic text that says it is impermissible (haram). In this case, it was authenticated in Sahih Al-Bukhari that the Prophet (peace and blessings be upon him) asked `A’ishah (may Allah be pleased with her) to be like Umm Zar` who pierced her ear.
With that in mind and that no prohibition came to the number of piercing ear, it should be lawful to pierce ear twice or more.
Allah Almighty knows best.