It's become quite a popular theory among Game of Thrones fans that Sansa Stark will end up as Queen of the Seven Kingdoms. There's little proof that this will happen, save for Littlefinger's involvement, and this is why I think that's quite unrealistic.
-Littlefinger's involvement in her life is purely done for his own benefit. We don't know his plans for Sansa, but making a rough guess, it's something that will actively benefit Littlefinger, and not necessarily something designed to boost Sansa's power.
- Sansa is widely thought to be guilty of Joffrey's murder. Her hairnet being at the scene implicates her in his murder, so everyone thinks that Sansa's a kingslayer (at least partly). It's unlikely that lords would welcome a kingslayer as their Queen. There's a reason she's disguised as Littlefinger's bastard daughter, Alayne Stone
-Unlike most of the other claimants (Dany, Aegon, Stannis etc.) she doesn't have an army or have Lords sworn to her. Say what you want about Dany and Stannis, but they have armies at this stage that are already sworn to them, and Stannis now has the allegiance of the North as well. Aegon doesn't have an army as of yet, but Varys and Ilyrio are trying to put him on the throne- and they're the kind of guys who MAKE armies, as soon the flip-flopping Lannisters, Tyrells, Tarlys etc. will all flock to them - maybe of questionable loyalty, but huge armies. Sansa doesn't even have anyone to declare her as Queen, so she is quite far behind. She doesn't really command any armies.