Hmmm, I guess the process will need refining.
Both have to show in person in KL! That might be trickier if people are not living in KL. And having to produce all the documents every 6 months seems onerous. Kind of shoots a hole in my plan. But let's see what comes back.
I guess the theory for her to apply in her own name could work. But I'd have to transfer 350,000 MYR in her name. (Would a joint mother/son account with twice the amount work?) And then transfer 10,000 MYR per month for at least 3 months into her account to show an off shore income. I wonder if that'd float. The 10,000 MYR per month offshore income would be incoming from her son. Reality is I couldn't sustain the 10,000 MYR for too long. She'd be living on more like 3,500 MYR. But I guess once she had the visa then we'd be fine until the next renewal.
Seem kind of silly to have to jump through those hoops, no?
As a family(me + wife + mother) I have no problem to leave 300,000 MYR on fixed deposit in Malaysia.
As in all things with all Government Institutions anytime someone tries a new approach the bureaucrats get nervous.
I have no real knowledge but do not see anything wrong with you financially supporting your mother to obtain her own MM2H visa on her own volition. Probably more guaranteed than from Goldman Sachs....or others...

If you have the required substantial amount in a joint or separate account for her to qualify, and evidence of monthly income, that should satisfy the requirement. Where it comes from should not matter.
I personally had difficulty substantiating my income as it was dependant on the markets and dividends etc. Joy-Stay managed to manipulate the income requirement to satisfy the Government. I do suggest Joy-Stay would best assist your mother to get the visa if you are not in a position, at this time, to administrate everything.
The main issue is that your mother will need to deposit RM 150,000 in a bank in her name in Malaysia, and it cannot be allowed to reduce, unless in special circumstances.
Once she receives her MM2H visa there is no further requirement to maintain a RM 10,000 per month income...no-one checks. She can live as well or as frugal as she determines.
When you wish to exercise your own MM2H and get your visa, it is possible to collapse hers if you do not wish to maintain her RM 150,000 deposit or, as you already suggest, just keep both MM2H visas separate and eliminate the Dependants 6 month renewable visa issue.
btw...for what it is worth..
I have already established using my MM2H fixed deposit (interest bearing) as part of HSBC's requirement to maintain their Premier Global Banking facility. I was thus able to collapse my other FD (non-interest bearing) that was previously needed for HSBC's Premier Bank facility.