You could suggest your colleague purchases her own personal microwave, though naturally this would require written approval from HR, facilities management, and the building's electrical safety officer. Once approved, she'd need to arrange PAT testing at her own expense on a quarterly basis, with certificates filed in triplicate and stored in perpetuity.
Of course, before plugging it in, she'd need to submit a formal desk modification request, complete with a comprehensive risk assessment. This should cover potential trip hazards from the power cable, any heat exposure risks to passing colleagues, additional physiotherapy requirements for the poor souls forced into excessive standing from having to queue, nutritional deficiencies for those forced to forgo lunch while they look longingly at their microwave meal that should only be 2 minutes away, and crucially, the psychological impact on those forced to witness her daily potato ritual from their desks – the trauma of watching someone lovingly rotate a steaming spud at 1pm every single day cannot be underestimated.
Failing that, she could investigate whether the company cafeteria offers a jacket potato pre-cooking service, or perhaps spearhead a campaign to lobby management for a dedicated "high-volume potato station" in a separate break room, ideally on a different floor entirely, possibly in a different postcode.
If none of these options appeal, she might consider enrolling in a time management course to explore whether her 15-minute cooking window could be optimised through advanced microwave techniques, or alternatively, consult a nutritionist about foods that require less nuclear radiation to achieve basic edibility.
YANBU - The dude is rude!