All these days aarti was doing all these things with love and care. and i feel only the song part was pre-planned n may be the kids playing with yash. but the water scene was due to ansh's intention to join his mother into the game n there aarti was herself n not arpita. since yash was so occupied with arpita's memory he relates every actions of hers to arpita. may be the morning song effect. this time even yash joined with them so that made the difference a lot. otherwise aarti was the same like before she was caring, playful and 😳 when she sees yash. not much difference in her approach.
Even earlier when the kids wanted to play in the bedroom jumping on the bed she was willing to allow them to play but yash got pissed up n send them out. n many times she had tried to take them out but she cudnt. during her initial she and ansh faced lots of problems from gayatri even them she never left the girls unattended. she made ansh to ready by himself n took care of the girls.
Remember the scene when she wanted to put colour clips on their pony she didnt do it bcoz gayatri said but she did bcoz she kows y she is here n wat girls are missing n wat are yash's expections.
Her nature is to hide her sorrows n never show before anyone. she kept ansh happy burrying her past n even here how much bua and gayatri tortured her she never showed it towards the girls n never differentiated them from ansh. she was always on step ahead of yash in accepting the other's kid during the mall scene scene even she when was not fine with yash (maansi's POV) she introduced with them as their new mom n during the wedding though she was such horrible situation regardig hiding truth n abt yash' character she never avoided the girls smiling r enquiring them whether they got hurt r not when ansh fall down.