Jacqueline Morton spent the whole of the last lockdown shielding due to her condition - which puts her at high risk of hospitalisation if she contracts the virus.
The mum-of-two says before half-term the school told her that her 14-year-old son could study online from home however this changed as school reopened.
Outwood told the worried mum she would be fined if she kept her Year 10 son home.
However she received a phone call from the school on Wednesday informing her that her son would have to self-isolate at home for 14 days.
The teen had been identified as a possible close contact of at least one of two confirmed coronavirus cases at the school.
Now the anxious mum is having to isolate from her son - who could be carrying the virus - by sitting at opposite ends of the room during meals and existing in separate rooms at all times.
Finance worker Jacqueline described how the situation she and her son now found themselves in had highlighted her original concern.
She said: “I had already pointed out the risks to the school and now I’ve been proved right.
“If my son does have the virus I don’t know how that’s going to affect me - he’s in his bedroom most of the time and luckily we have a second bathroom he can use.
“But we have to be at opposite ends of the room at dinner and I absolutely hate doing this - you need someone to comfort you at a time like this.
“It’s just completely ridiculous to have a blanket policy - a bit of understanding and sympathy here would not go amiss.”
Jacqueline, 43, told how she and her son were now isolated from each other after an ‘awful’ year during which four loved ones - including her father, mother-in-law, grandmother and a close friend – had died of causes not related to Covid-19.
She said: “It’s really hard for my son but I’m just so proud of how he’s handled this - the maturity he’s shown over the last 10 months has been phenomenal.
“I just don’t understand the school’s U-turn over this - I’m not the only one this is affecting and people’s voices need to be heard.”
A spokesperson for Outwood Academy Valley said: "We have been in contact with the student's mother this week to discuss the matter with her and have offered our support to the family through this tough period.
"The issue in question arose from us explaining the official government guidance regarding absences during this period, which is children who live with someone who is clinically extremely vulnerable, but who are not clinically extremely vulnerable themselves, should still attend school, but we believe we are moving on from this now and we will continue to support members of our academy community as best we can."