Translation:I got this wallet from my mother.
Something を 母にもらいました
The complete form = Something を 私が 母に もらいました
Let's simplify this into a formula, A が B に もらいました
therefore, A received from B.
If A or B is 私, it can be omitted including the attached particle.
In the wallet sentence, since A が is omitted, it is implied that "I" received the wallet. Of course you could change A into siblings, sisters, brothers, other people that received the wallet.
Now if you want to say 母 is the one receiving from 私, just swap them around, by saying 母が もらいました [ 私に is omitted ]
Finally, the rules for あげる and くれる are slightly different yet confusing however.
The rules with あげる and くれる aren't that much more confusing, just a few more extra points to consider before using compared to もらう. They both just mean "to give" with no connotation of receiving in the sense of もらう, but あげる is for you or someone in your group, and くれる for someone who isn't you or in your group.
私はあの人にお金をあげました。(I gave that person money)
あの人は私にお金をくれました。(That person gave me money)
If there is any challenge, it would be deciding who falls inside your group and who doesn't. I suppose whether you use あげる or くれる is based on whether the giver is more similar to you than the receiver or not. That is all dependent on our favorite c word.
Report it, if you think it should be accepted. Because the tree is new, they need us to send things in. There are many ways to say things, and they can't possibly predict them all. With this one, though, I believe the wallet is technically the subject. So I'm not sure if it would be accepted or not.
I think this sentence is a good example of using the honorific お/ご. Most of the time in this course, you see it in cases where the item it's attached to belongs to someone else, but here, the item it's attached to belongs to the speaker. This is because, even though the speaker owns the wallet at the moment, it was selected and given by someone else (the speaker's mother) and and due to that, speaking well of the item reflects well on the person who gave it.
Certain verbs "take" certain particles eg. が often goes with potential verbs potential forms of verbs like できる、話せる etc. Here もらう and に work very similarly to how passive voice verbs work. The subject is marked by は or が and に shows the means by which you received something, in this instance the speaker received the wallet by way of their mother. In this instance にis not showing direction, so something is to or for, a specific day or time, or purpose えいがを見に行きました (I went to watch a movie - or for the purpose of watching a movie). Here に shows the means by which something was received or the person by whom or from whom something was received - it is loosely translated as by or from but from is more natural in English. に tells us who helped facilitate the action. Hope this helps/makes/sense.
I said "This wallet is from my mother." - is there a way this is grammatically different? Usually I understand why the translation could be taken another way, but aside from thinking the person somehow stole the wallet, I don't see how this could be meant any differently than that she gave it to me.