You'll have to move the writer closer to the free IDE connector on the existing ribbon cable - depends whether you, (or your mum), can be bothered.
Spacing on IDE cables seems to be pretty standard, so if it doesn't reach both devices with the existing flat ribbon cable, a rounded version won't make any difference.
You only have one IDE port on the motherboard, so both the existing Maxtor HDD and old IDE DVD need to be plugged into the same cable, (as it was previously).
If you want to go this route, grab another picture of the inside as it is now and we'll suggest device positioning to get everything going, (might be time to vacuum it out again anyway
).