Please tell me, could give my 12 yr old daughter zantac (ranitidine) 150?

Yes, but....: It is safe to use this dose for a 12 year old, but my question is why? Have the symptoms she is experiencing been investigated so that you know this is the appropriate medicine to give? These medicines, even though many now over-the-counter, are not without side effects. Long term use is not recommended for her age. So how will you know how long to use it. Suggest you talk to her pediatrician.