How is it possible to reconcile good treatment of non-Muslims with being careful not to fall into temptation, especially when admiring a non-Muslim girl, while recalling the Quranic verses that prohibit marriage to polytheistic women, and is the intention to advise her to convert to Islam and then marry her considered as not purely for the sake of Allah?

One who loves Allah is someone who prefers what Allah loves over what they themselves love, avoids following whims, and perseveres in obedience and supererogatory acts. Your love for Allah and your fear of Him, intended to extinguish the fire of temptation in your heart, are among the fruits of His love, Glory be to Him. Your residence in a land of disbelief and your studies in mixed universities open the door to temptation. Scholars have emphasized the seriousness of these matters and have not permitted them except out of necessity or severe need. The temptation your heart feels for this girl is clear evidence of this. There is no harm in your intention to marry her if she embraces Islam, as marriage extinguishes the fire of lust and cures infatuation. It is permissible for you to invite her to Islam with the intention of marrying her, provided you adhere to Islamic guidelines. It is preferable that she be invited by women like her, because some cases that began with da'wah (invitation to Islam) ended in committing what Allah has forbidden.