HBC 1.1.0 is fine on Wii.
Newer version contains mostly fixes for vWii. (it doesn't even trigger an automatic update on Wii if you are still using 1.1.0).
if your HBC is using IOS61, and you are on 4.3E, then you should already have IOS58 installed.
Just re-install HBC.
download
hackmii installer, and launch it from HBC (don't put the boot.elf on the root of your SD card, but on apps/hackmii_installer/boot.dol (or boot.elf if there's no dol provided)
select "install HBC" and it will replace it. It should tell you that it will use IOS58 before installing.
After HBC is updated and use IOS58, you can install a patched IOS (d2x cIOS).
d2x cIOS full pack for Wii
extract to a folder in your apps (ex: sd:/apps/d2x_installer/)
run the installer from HBC and install this :
common setup :
slot249 : d2x v10 beta (r52 or r53), base 56, version 21008
slot250 : d2x v10 beta (r52 or r53), base 57, version 21008
r52 = better compatibility
r53= users following guide blindly and having issues later.
My own recommended setup :
slot249 : d2x v8 final, base 57, version 65535
only one cIOS is needed, v8 (not v10, latest is not always better), in slot 249 with base 57, with version 65535 (so she can play retail discs without update message) and you will have the best compatibility and no need to mess the settings later, that's a lot easier if your niece doesn't understand hacking ! just make it easier for her. ONE setup, NO worries.
that's all !
no modmii needed
but if you prefer modmii, it will install different cIOS and your niece will have to change the setup for few games. I'd recommend going with my method : update HBC, install 1 cIOS.
remove both hackmii and d2x installer after you are done, so your niece will not mess with these programs.
After that, be sure USBLoaderGX is installed as forwarder and not as a full channel.
you can follow this guide to replace it :
https://gbatemp.net/posts/6478222