Is it acceptable for a widow to ask in reverent prayer for a BOAZ to come into her life?
It is 100% allowed to daven for a shidduch
Rabbi Moshe Taragin told our Kollel that when one davens, sometimes they get distracted by everyday things, everyday troubles, even if it's not so important for example they want to do well on a test or the likes. They should focus on those worries and bring them before Hashem.
In davening we are supposed to pour our heart out to Hashem Shulchan Aruch (98:1). We all have concerns that we are worried about. In the shemoneh Esrei, there is a brachah called Shema koleinu (שמע קולנו). In this holy brachah we ask Hashe to hear our prayers and beseech him with our problems, worries, or concerns.
There is also nothing wrong with davening to Hashem for your personal needs. That is one of the main reasons for prayer. When we don't know what to do we pray to Hashem for anything.
There is a mitzvah called Peru u'Rvu. One can not fulfill this mitzvah if they never get married. If they are worried about not being able to fulfill this mitzvah, then praying to Hashem to help one fulfill a mitzvah is what many do during davening.
If I was not clear please comment down below and Be'Ezrat Hashem I shall answer.