My client dropped her mktg agency and Organic traffic dropped by 50% in 5 months

I started doing Google Ads for a client and I help her occasionally with SEO but nothing too big. She was working with an agency that built the website and had to drop them because of budget constraints The website is very nicely done and we haven’t made any changes at all … but in the past 5 months organic traffic dropped by 50% , including home page and main pages. It’s a significant drop out of the blue, specially when nothing has been changed (that we know of) They also came to us to tell us “your traffic went down by 50%” and how we need them back … which sound fishy , but the traffic loss is real Any recommendations of what to look for to understand the drop? And something they could have done and we are missing ? Unfortunately she has no budget to pay the agency TIA