I believe on these 4-stoke mower engines that you pour the old oil out of the same oil filler hole that you'd also add oil to. see: https://www.youtube.com/watch?v=qk1PsuHJ... http://powerequipment.honda.com/support/...-manuals/lawn-mowers
If it had water damage, I am shocked she even touched it. iPhones have built in water exposure indicators, and if they show water exposure, many shops (including Apple) won't touch them. As far as what you should do, maybe look at another iPhone. If you used iCloud backup or backed up to a PC/MAC using iTunes, then it is a pretty easy transition.
Do not change or check the AC power adapter, it is a bad battery. Replace it. The ones on Amazon will either be 3rd party generics (all those batteries you see in the $15-35 range), 3rd party name brand or genuine HP. The generics will more than likely fail pretty quick. For 3rd party "name brand" (eg. Duracell) you are also paying more. For genuine HP, you will be paying quite a bit more. If buying on Amazon, look at the reviews for the battery as well as seller feedback. That will give you a good idea of the quality of the generic. example of 3rd party name brand batteries https://www.batteriesplus.com/battery/la...-packard/pavilion-dv6-series/pavilion-dv6=6135dx
Sounds like it initially had a bad battery. I'd say try opening up the Chromebook, unplug the battery and then plug the AC in and see if it fires up. If it does, while the AC is plugged in, plug the battery back in. If not, I'd recommend buying another Chromebook because they are not economically repairable (the cost of repair is higher than a used, working Chromebook).