Just because she is a neighbor doesn't mean that she will have an IP address that is anything similar and the chances of only the last octet being different are virtually zero.
Having the same ISP is also irrelevant.
Feel free to blindly scan random IPs but in all honesty it will be a fools errand.
You're best bet would be to bump in to her and casually ask her about the system. Say you have seen the stickers and are thinking about installing something similar. You could ask or she may offer to show you how it works.
If she does fain ignorance over how she is able to view it remotely and ask her to show you how that part works.
if she does she will probably open up an interface on her phone. if so you need to look for the DYNDNS or similar name that she uses to connect in the app. Once you have that you are half way there. Then assuming the access isn't locked down to specific devices you only need to figure out her password or hope that the system has a backdoor.
In all honesty GIVE UP and move on. The chances of you getting anywhere are so low it isn't worth trying.