What about...
Getting a Fitbit each and you can put it on challenge mode and you challenge eachother either over a day or week and the winner is the one who does the most steps. We do this with about 16 of us in work over the week and the winner gets a novelty £1 shop prize but it's fun
What about intermittent fasting - have a look online different plans are for different ages but a plan looks like you can eat whatever foods that want within an 8 hour window
Avoid 'empty' calories - pop, sweets
Have what she wants but smaller portion - even things like butter still have it but get the lighter version and use half as much. Mayo get the lighter version and use half as much. If she eats garlic bread and would have 5 pieces then cut it down gradually to 3 pieces.
Cleaning tea - look online about chamomile / ginger tea - it can really help with loosing weight
Getting good sleep - get her sleep in check, comfy pillows, bedding, lavender under the pillow/spray
Try yoga at home together if you don't want to do a class - loads on you tube - make it fun. Start with 10 min sites a day and work it up
Have a look at mini bikes - people use them in their office and peddle while working she could do that while watching tv
Mindfullness - look on you tube/ get self help books - perhaps there's a reason mentality why she is struggling with her weight
Hypnotherapy - honestly this can work so well and whip those bad eating habits out the window very quickly . My sister went for smoking had theee sessions and now she can't even smell a cigarette without feeling sick
Get off social media - if she's looking on Instagram etc at all these skinny women that will be motivating for some but highly drama gong and demotivating for others
Avoid snacking - eat o lot at meals times 3x a day
Wall exercise - have a look online it's a new fad but apparently works - it's where you work out using the wall in the comfort and privacy of your own home and no equipment required