What was the turning point for Naina's feelings for him?

We all saw Naina thinking that whatever Sameer did ... that was meant for himself only... or again it's some sort of a new bet for him...

Arjun wala incident.. she realized it was her brother at fault not sameer.. usne to kitna kuch kiya.. as she said sameer mushkilo se bhaga nh usne unka samna kiya.. n rhi bat sameer ka pyar realise krne ki to at every point sameer showed his caring side n love side..

When she realised Sameer told her truth about Arjun's recovery that was the end of her dilemma to forgive Sameer or not..

I feel it was the chachi chachi patchup...

Lots of reasons
PTA meeting,
Chacha-Chachi Patch up,
Arjun's truth.

It was all a build up. One cannot be angry with the person you love for long. All three played a significant role along with the constant nagging of Preeti. Preeti kept appreciating Sameer in front of Naina which played on her mind and remained. If u notice she said the same thing to Arjun what Preeti said "Sameer sabki taane sunn raha hai this portion. Munna Pandit too kept saying Sameer Badal gaya hai. To add to this Sameer kept winning everyone's heart one by one in the family.

Also..Shefali told her that Tumhe toh jhute logo se nafrat hai na. That also affected her. She cannot hate someone she loves. My interpretation.

Later she wanted to say sorry and thank you to Sameer but Sameer troubled her and said "Maaf kar dena chahiye, tadpana nahi chahiye then she decided to show her love and the bottle scene happened

Now Sameer being insulted and thrown out of her house after doing so much for her family (including Rakesh felicitation and ego booster at the PTA and Arjun's service) and his efforts to win her heart completely. He managed it and now Sameer resides happily in that heart of hers.

I think it was all of it...building up gradually...breaking the walls of her anger...gently healing her heart...she was melting all the way...through and through. she voiced it to herself only after chacha chachi patch up VO said it was getting difficult to stay angry with him...she allowed him to pin up her dress even before Arjun's truth came out...that was a sign she started trusting him again...she came to talk to him after he was scolded by Rakesh in front of everyone...she patched up already then...forgiving and healing is a process and then it reaches its climax in an instant and for her the instance was when he declared his marriage plans already infront of so many people indirectly though...when she smiled forgetting her anger...but she let her guard completely off loose when Shefali said those words to her...you hate people who cheat and betray...those words made her see through her own weakness and partiality and she decided to apologise to Sameer.

I completely go with Delightful n Endlesshope answers...i feel it all started with the felicitation award that let her guards down that day...She was vulnerable n saw Sam in a different light...Infact her Vo did acknowledge him wholeheartedly!

I completely agree with @Delightful and @Endlesshope.

i feel these are the reasons

It started with pta meeting... Her long time dream was fulfilled because of him... Then helping chacha chachi... Defending her in front of everyone made her look at him in a completely different light... After that she ws happy to be around him... Then arjun's lie made her away frm him again... When arjun ws exposed she started seeing the picture clearly... Hw genuine sam was in his efforts... Arjun's lie exposure was the last push needed for naina... After that there was no turning back for her... Her love for him was completely rekindled... She started making moves... Now they both knows each other ver well... Such a great journey it was. 😊