Whenever certain phone connects ping skyrockets

[rayaans]

My sister has a Samsung galaxy j7 prime. I've noticed that whenever she is using her phone, my ping skyrockets to 1000+ and when she's not, I average around 50-60 ping on CS:GO. I've tried everything to my knowledge to fix it but it seems it's out of my ability.
I've tried QoS on my router, which is a DSL-2750U. It requires a DSCP mark and I've selected EF(101110) after reading about the mark somewhere (it said it prioritized gaming) but I haven't noticed any big difference. Also, I read a thread that said it was google+ however she does not have google+ installed. I'm not very good with networking so I don't know what to do. Please, any help would be greatly appreciated. Thanks in advance.

 

[punkncat]

Our son's previous iPhone knocked out our LAN every time he turned on the WiFi, as well as one of his Apple pads. I never could figure the issue out, but it resolved when he traded up for a newer phone and when the pad went to a newer OS.
We actually paid a part of his data plan so that he didn't have to use WiFi while we were on the network.

 

[rayaans]

Still not solved..