Where does your Mom live? If it's in the U.S. you can call the State Office that handles senior citizen issues and ask them to do a check on her. If she's low income she may be eligible for a case manager. Tho, since she has a maid, she may have to pay for the service.
I'm not sure I'd get her a dog. They are a lot of responsibility and work. She would have to be the dog's alpha leader and train her to obey her. Otherwise a dog will take over and not be led by her. She would have to walk it at least a couple of times a day, especially if it's a large dog. Some small dogs could be let out but that wouldn't be ideal and probably wouldn't work unless her yard is fenced.
I suggest you need to talk seriously with your brother and get him involved. Perhaps he's not as concerned as you are and since you're not there I suggest you'll have to rely on him and his evaluation.
A security alarm also has to be managed. If she's forgetful, that won't help. She has to remember to turn it on and off at appropriate times.
You can have one installed that is connected to a security office who will then call her and if there's a problem, they'll call the police. The negative of having one is that after one or two false alarms she will get charged for them. It's been my experience that many people, and not just older ones, have many false alarms because they don't pay attention.
Please know that it's highly unlikely that anyone is going to break into her house and steal from her and even more unlikely that anyone is going to hurt her. If the maid's son or the maid steals they'll do it while having a legitimate reason to be in the house. She won't know it's happening. The alarm system will not prevent that.
Later: I'm not trying to discount your concern. I'd be worried too.
How old is your mother? I'm 70 and have friends who aren't able to move around because they don't move around. It really is true that if we don't use it, we lose it. That is especially true for walking/moving around. And it's hard for some people to keep moving when they don't feel well. Not feeling well becomes a vicious circle. We feel sick so we don't walk and then we feel sick because we're not walking and on it goes.
One friend has been over weight her entire adult life and this has ruined her knees. She limps because of the pain. I sprained my knee and my ankle many years ago and a couple of times a year they hurt and I limp.
I also have a friend with diabetes. She has peripheral neuropathy which means she can't feel her feet as well as she needs to to be able to get around easily. Her doctor wants her to keep walking but she's frightened of falling and so sits in her chair all day long. It's so sad.
These are just a few of ideas and may not fit with your mother at all.