There is another reason I can think of as to why Rika is training a 3A-Eu-3S, and I always thought she might.
This season, her maximal possible (feasible) layout is
4S
3A+2T
3A
3F
3Lz+3T
3Lz+Eu+3S
3Lo
Technically, it's probably a better idea to put that 3F last instead of the 3Lo as her 3Lo has caused a few problems while her 3F hasn't, but anyway that's not a big deal. The question is, what can she do next season? Once she puts the 4T into her program, we'll have
4S
4T
3A+?
3A
3F
3Lz+?
3Lz+?
One option is to do two 3Ts instead of two 3Lzs, which isn't that great points-wise but avoids the issue of having a loop combo (she's done them before). This option would leave
4S
4T
3A+3T
3A
3Lo
3F+3T
3Lz+Eu+3S
However, what happens, come Olympic season, when Rika wants to try another quad? Suppose her 4S is more stable than her 4T, which seems to be the case as she isn't doing a 4T this season. If she wants to do two 4Ts and two 3As, she runs into obvious problems with her combinations; what to do about the extra 3T? So, I propose the following layout instead.
4S
4T
3A+3T
3A
3F/Lz+3Lo
3Lz/F
3Lz+Eu+3S
depending on which 3Lo combo she likes more (she's done both before, but I reckon her 3F combos are better than her 3Lz ones)
This gives, for Olympic season,
4S/T+?
4T
4S
3A+?
3A
3F
3Lz+?
And now we have another problem. I strongly doubt Rika will do a 4S+Eu+3S, and definitely not a 4S+3Lo, so she's probably going to go for a 4S+3T. She's also not going to do 3A+3Lo, which means she has to do 3A+Eu+3S. That finally leaves
4S/T+3T
4S
4T
3A+Eu+3S
3A
3F/Lz
3Lz/F+3Lo
The only way she could improve on this is do a different quad, which I doubt is happening. I don't know if she gets enough spring to do any other quad, but I may be wrong.
Anyway, I feel like Mie Hamada is looking ahead enough and recognising that Rika will need this combination down the track, and it's great for strengthening her 3A anyway.