Mass Effect Legendary Edition review. (Contains massive spoilers.)

Again, you're assuming Shepard's body "landed" close to where the Normandy crashed... which is probably not the case given that he/she was blown away from the ship when it exploded and is seen falling or going into an orbit around the planet alone... away from the ship.

Again, you're assuming that Hannah's asking for updates would result in something more... As long as the Alliance could not find a body (which they couldn't because the Shadow Broker and then Cerberus had it), the only response she would reasonably have gotten was that Shepard was MIA - Presumed Dead.  AFAIK, there is no actual set time limit in Alberta for when a missing person can be declared dead in order to allow for things like their estate to be probated, but that seems to be what happened with Shepard ultimately since a memorial exists.  That may be why Bioware wrote the story such that Shepard was missing for two years.  People process a "missing person" at different rates and it also depends on the circumstances under which the person went missing.  For all we know, it may have been Hannah's decision to eventually "give up" on the search for her son/daughter and move forward with things like processing the estate and having a memorial... again, considering that the last place he/she was seen was aboard a ship that was exploding violently (a circumstance that practically no one would be expected to survive without an escape pod).

I also tend to think that the Normandy Crash Site DLC compresses the debris field from the ship into a much smaller area than is realistic.  In reality, much more of the ship would have completely disintegrated as it fell from orbit around the planet and the debris would like be spread over many, many miles, perhaps even hundreds of miles... given that it broke up in orbit (since even planes that break up in the air can spread debris over many miles.

Those are the questions you insist on asking... We don't know if Hannah asked them and, if so, what answers she was given.  That's not written into the game.  Head canon whatever you like... and I'll head canon whatever I like in those regards.  You love Cerberus and hate the Alliance, so you're going to head canon to support your biases... but it's still your head canon.

All we know is that the Alliance did not find the body.  They did eventually found the crash site; but did not find 20 dog tags and a helmet (unknown whether or not it was the helmet Shepard was wearing at the time of the crash, since Shepard obviously has acquired more than one in all the games.)

We know that A/K was on Horizon as soon as Shepard sees Anderson... which can occur immediately after Freedom's Progress.  We know that the Alliance was in the process of setting up a Gardian Laser.  Another thing we know... Delan told us outright that he thought the Collectors were "just propaganda to keep them in Alliance space." - so obviously someone (and it wasn't Cerberus) was telling them about the Collectors being a threat to remote colonies before Shepard gets to Horizon.  We know that the Alliance was not stretched very thin, as TIM claimed.  We know that Shepard did not present Veetor's evidence to Anderson or the Council on the Citadel.  We know that TIM knew the Collector Ship was a trap.  We know that Dr. Chandana's team had been established on the Derelict Reaper long enough to become completely indoctrinated and turned into husks at least 4 days before Shepard arrived (because the VI tells us the ship had gone 4 days without a workplace death).  We know that TIM suspected the Collectors were involved even before he sent the team to Freedom's Progress (because he says as much).  We know he suspected they used a special IFF to get through the Omega 4 relay (again because he says as much).  We know he doesn't tell Shpeard about the trap on the Collector Ship nor does he mention the IFF until after the mission.  We know both Liara and Cerberus knew for 2 years that Shepard was not dead... and did not inform the Alliance of that fact.

We also know that, upon waking up, the only information Shepard gets comes from Cerberus... so, ultimately, he/she agrees to work with Cerberus without being able to verify for himself/herself whether or not the Alliance is doing something already or not... and that alone makes him/her a willing traitor to the Alliance.  The onus was on Shepard to talk with Anderson and the Council BEFORE agreeing to work with Cerberus.