Both excess suds and a partial drain restriction are plausible. **The most useful distinction is whether liquid water rises in the standpipe along with the foam.** The late-cycle timing alone won’t identify the cause.

Six months of the same routine can still lead to a new problem:

- **A restriction develops gradually.** Lint and residue can reduce capacity in the trap or laundry branch until the washer’s discharge overwhelms it. Other fixtures backing up would make a shared downstream restriction more likely.
- **The same detergent dose produces more foam.** Check whether she opened a new bottle with a different concentration, changed bleach, or had a water softener serviced. Whirlpool identifies excess detergent, non-HE detergent in an HE washer, very soft water, and splashless bleach as possible causes of excessive suds. [Whirlpool troubleshooting guidance](https://producthelp.whirlpool.com/Laundry/Washers/Top_Load_Washer/Cleaning_Performance/Excessive_Detergent_or_Suds).
- **Detergent residue accumulates.** GE notes that suds remaining near the end of a wash cycle can indicate detergent buildup in clothing. [GE residue guidance](https://products.geappliances.com/appliance/gea-support-search-content?contentId=17992).

On the service call, I’d proceed this way:

1. **Watch a discharge.** Rising liquid and slow recession point toward inadequate drain capacity. Foam emerging while liquid stays down points more strongly toward oversudsing; both problems can coexist.
2. **Run an empty rinse/drain with no additives.** Residual detergent may require several rinses. Once the discharge is clear, repeat at the washer’s actual pumping rate. A low-flow garden-hose test can miss a restriction.
3. **Check the hose position against the washer’s manual.** Excessive insertion is a recognized installation issue. [GE installation troubleshooting](https://products.geappliances.com/appliance/gea-support-search-content?contentId=17532).
4. **If clear-water discharge backs up, investigate the trap and branch**, then the shared drain according to what the other fixtures show.

My starting hypothesis would be excess suds if it’s strictly foam, and a developing restriction if the water level also climbs.