Gradual withdrawal will work. It'll take time and patience, it's no quick fix, but atvkeast you'll make consistent progress in the right direction.
Firstly GW means baby trusting you will give as much comfort as she needs all the way until she's asleep. Over time you reduce the level of comfort needed.
So your start point is lying on the floor next to the watching Kate Perry videos (?!). I assume this is watched on your phone?
Going to sleep in front of a sxreen can be quite damaging, so I'd stop that immediately. Do everything else the same, stay by the bed. Coo and fuss over her as needed and stay until asleep, but just not using the phone/tablet and give extra reassurance instead.
Wait however long it takes for her to accept this - that you'll always stay with her and help her sleep, but no Katie Perry. If she likes background noise then a bedside fan is good source of white noise.
This might take several weeks, be patient. Always offer enough comfort and stay until asleep. You can't move into tackling the next bit until this is done.
So to tackle lying on the floor to get her to sleep, it involves tiny changes every few days.
Start lying on the floor facing the cot, stay until asleep.
Begin turning to face the ceiling (not the cot), stay until asleep. If upset, turn to face baby and resettle, then move back into your back looking at ceiling. Stay until asleep. Do this for as many nights it takes to no longer be an issue. It might be a couple of nights or a couple of weeks.
One accepted, make another small change. Settle in cot, lie down, turn and face away (but still next to) the cot. Turn back when needed to resettle, but turn away when settled. Stay ubtil asleep.
Once this is accepted (may be a few days or a few weeks), make another change. Start rolling away from bed slightly.
Once accepted, start sitting up. Still only a step away from bed, but not lying down.
Once accepted, sit further away. Then sit facing away. Then try standing. Then standing facing away from cot. Then standing further away. Then standing by the door.
In each of these changes you always stay until asleep. You also can go backwards down your levels of withdrawal of extra reassurance is needed. Just progress back up the withdrawal once settled.
This isnt about baby being denied any comfort. its about gradually teaching baby to need less reassurance.