I'm inclined to believe her, to be honest, until proven otherwise.
Russia, even in the modern age, has had a reputation for covering up offical accidents (K-19 anyone?) well past the old Soviet era. I don't think it is a stretch at all to think that they would look at a site like this with trepidation and try to discredit it or the author.
The poster to Neil Gaiman's site, for example, offers up lots of what look like facts (organized trip, officials debunking the site) but without any real hard data. There are no quotes from officials that someone could follow up on, no names of people he spoke to, no copies of the tickets, etc. We are expected to take his statements at face value simply because he says so and is ostensibly writing about Chernobyl. Even if I search him out and find that his book is now out and on the shelves, that doesn't mean that he is somehow more qualified than the person putting up the site. Imagine if writing about liberals made Ann Coulter an expert on them. Shudder.
She makes no claims at being a journalist or scientist, has no ads on her site and simply takes donations via Paypal. With all the snappies and videos on her site, you know her bandwidth costs are going to be pretty high and unless her site sees more donations than everyone else trying to earn a living that way, she likely doesn't even cover the costs of hosting the site. She was Slashdotted a couple of years ago, so you know that a zillion people visit the site ... and that ain't cheap.
So, no real financial incentive, pictures on the site show the bike in situ, the site is still up (if someone really wanted it down, it would go down), scenes from the stills match scenes from videos taken in the week after the disaster, etc. Like the person who submitted to Neil Gaiman's site said: why would anyone go to this length?